\documentclass{article}
\usepackage{fp}
\input pstfig
\begin{document}
$
\def\mytheta{130}
\FPeval\myangA{round( (180 - \mytheta) / 2 : 4)}
\FPeval\myangB{round( \myangA + \mytheta : 4)}
\def\myR{3}
\pnode(0,0){O}
\pnode(\myR; \myangA){A}
\pnode(\myR; \myangB){B}
\pnode(\myR; 90){H}
\psarc(O){\myR}{\myangA}{\myangB}
\pcline(A)(B)
\psset{labelsep=0.2ex}
\Aput{b}
\thinline
\pcline(H)(H|B)
\Aput{h}
\dashline
\psline(A)(O)(B)
\noneline
\pcline(O)(A)
\psset{labelsep=0ex}
\Bput{R}
\uput{0.2}[90](O){\theta}
$
\end{document}

